This invention relates generally to immunoassays for the detection and differentiation of antibodies to Human Immunodeficiency Virus Type 1 (HIV-1) Group M, HIV-1 Group O and Human Immunodeficiency Virus Type 2 (HIV-2). More particularly, the invention relates to novel antigen constructs useful as reagents in such assays, as well as polynucleotides, DNA clones, expression vectors, transformed host cells and the like which are useful in the preparation of such antigens.
Detection of HIV infection in a patient, and characterization of the viral type, are typically carried out using immunoassays which rely on the highly specific interaction between antigens used as reagents in the assay and circulating antibodies in the patient's serum. The immunoreactivity of patient antibodies with some antigens, and to a lesser extent or not at all with others, permits the identification of the type and subtype of the HIV which is present.
Currently, there are two major phylogenetic groups of HIV-1 designated as Groups “M” and “O.” G. Meyers et al., Human Retroviruses and AIDS 1995, Los Alamos National Laboratory, Los Alamos, N. Mex. (1995). HIV-1 Group M isolates further have been divided into subgroups (A to J) that are phylogenetically approximately equidistant from each other. Group M isolates predominate worldwide. The earliest reports about the sequence of HIV-1 Group O indicated that these viruses were as closely related to a chimpanzee virus as to other HIV-1 subgroups. See, for example, L. G. Gürtler et al., J. Virology 68:1581-1585 (1994); M. Vanden Haesevelde et al., J. Virology 68:1586-1596 (1994); De Leys et al., J. Virology 64:1207-1216 (1990); DeLeys et al., U.S. Pat. No. 5,304,466; L. G. Gürtler et al., European Patent Publication No. 591914 A2. The Group O sequences are the most divergent of the HIV-1 sequences described to date. Although HIV-1 Group O strains are endemic to west central Africa (Cameroon, Equatorial Guinea, Nigeria and Gabon), patients infected with Group O isolates now have been identified in Belgium, France, Germany, Spain and the United States. See, for example, R. DeLeys et al., supra; P. Chameau et al., Virology 205:247-253 (1994); I. Loussert-Ajaka et al., J. Virology 69:5640-5649 (1995); H. Hampl et al., Infection 23:369-370 (1995); A. Mas et al., AIDS Res. Hum. Retroviruses 12:1647-1649 (1996); M. Peters et al., AIDS 11:493-498 (1997); and M. A. Rayfield et al., Emerging Infectious Diseases 2:209-212 (1996).
HIV-1 Group M serology is characterized in large part by the amino acid sequences of the expressed viral proteins (antigens), particularly those comprising the core and envelope (env) regions. As between various strains of this rapidly-mutating virus, these antigens are structurally and functionally similar but have divergent amino acid sequences which elicit antibodies that are similar but not identical in their specificity for a particular antigen.
One of the key serological targets for detection of HIV-1 infection is the 41,000 MW transmembrane protein (TMP), glycoprotein 41 (gp41). gp41 is a highly immunogenic protein which elicits a strong and sustained antibody response in individuals considered seropositive for HIV. Antibodies to this protein are among the first to appear at seroconversion. The immune response to gp41 apparently remains relatively strong throughout the course of the disease, as evidenced by the near universal presence of anti-gp41 antibodies in asymptomatic patients as well as those exhibiting clinical stages of AIDS. A significant proportion of the antibody response to gp41 is directed toward a well-characterized immunodominant region (IDR) within gp41.
Infections with HIV Type 2 (HIV-2), a virus initially found in individuals from Africa, now have been identified in humans outside of the initial endemic area of West Africa, and have been reported in Europeans who have lived in West Africa or those who have had sexual relations with individuals from this region. See, for example, A. G. Saimot et al., Lancet i:688 (1987); M. A. Rey et al., Lancet i:388-389 (1987); A. Werner et al., Lancet i:868-869 (1987); G. Brucker et al., Lancet i:223 (1987); K. Marquart et al., AIDS 2:141 (1988); CDC, MMWR 37:33-35 (1987); Anonymous, Nature 332:295 (1988). Cases of AIDS due to HIV-2 have been documented world-wide. Serologic studies indicate that while HIV-1 and HIV-2 share multiple common epitopes in their core antigens, the envelope glycoproteins of these two viruses are much less cross-reactive. F. Clavel, AIDS 1:135-140 (1987). This limited cross-reactivity of the envelope antigens is believed to explain why currently available serologic assays for HIV-1 may fail to react with certain sera from individuals with antibody to HIV-2. F. Denis et al., J. Clin. Micro. 26:1000-1004 (1988). Recently-issued U.S. Pat. No. 5,055,391 maps the HIV-2 genome and provides assays to detect the virus.
These viral strains are, for the most part, readily identified and characterized using commercially-available diagnostic tests. However, concerns have arisen regarding the capability of currently-available immunoassays, designed for the detection of antibody to HIV-1 (Group M) and/or HIV-2, to detect the presence of antibody to HIV-1 Group O. 1. Loussert-Ajaka et al., Lancet 343:1393-1394 (1994); C. A. Schable et al., Lancet 344:1333-1334 (1994); L. Gürtler et al., J. Virol. Methods 51:177-184 (1995). Although, to date, few patients outside of west Central Africa have been found to be infected with HIV-1 Group O isolates, health officials fear the emergence of this subtype in other geographic areas as well.
Consequently, there is a continued need for new antigens, suitable for use in immunoassays, which alone or in conjunction with other antigens permit the recognition of all HIV-1 (Group M and Group O) and HIV-2 isolates and/or infections.